Hummingbird Gzip compression is not working (deflate module is enabled)

Hi, I've been installing Hummingbird on a few of my sites and have been getting this error:
Gzip is not working properly:
- Your server may not have the "deflate" module enabled (mod_deflate for Apache, ngx_http_gzip_module for NGINX).
- Contact your host. If deflate is enabled, ask why all .htaccess or nginx.conf compression rules are not being applied.

I contacted my host and they confirmed that deflate is enabled, and nothing is configured there that would stop .htaccess rules being applied to this site, also Gzip seems to be working on the homepage too.